Voltage grouping of energy storage units

ABSTRACT

Systems and methods for controlling an energy storage system are provided. In one embodiment, an energy storage system can include a plurality of energy storage units and a plurality of buses. The energy storage system can further include a control system that can be configured to receive one or more signals indicative of a voltage associated with each energy storage unit of the plurality of energy storage units. The control system can be configured to send one or more command signal to selectively couple each energy storage unit to one of the plurality of buses based at least on the voltage associated with the energy storage unit.

FIELD OF THE INVENTION

The present subject matter relates generally to energy storage systemsand more particularly, to energy storage systems that can selectivelycouple energy storage units to buses.

BACKGROUND OF THE INVENTION

Energy storage systems (e.g., battery energy storage systems) havebecome increasingly used to deliver power either as part of standaloneenergy storage systems or as part of power generation systems (e.g., awind farm, solar farm, gas turbine system) with an integrated energystorage system. Energy storage systems are unique in that energy storagesystems have the ability to both deliver and reserve energy forparticular services. Energy storage systems can include one or morebattery banks that can be coupled to the grid or other load via asuitable power converter.

Multiple batteries can be coupled to the same power converter via thesame conversion bus. However, batteries that operate at a lower voltage(e.g., due to cell failure) can experience overvoltage as a result ofbeing coupled to the same bus as higher voltage batteries. Whileindividual power conversion for each battery can help reduceovervoltage, it can lead to significant cost.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the embodiments of the present disclosure willbe set forth in part in the following description, or can be learnedfrom the description, or can be learned through practice of theembodiments.

One example aspect of the present disclosure is directed to an energystorage system. The energy storage system includes a plurality of energystorage units and a plurality of buses. The energy storage systemfurther includes a control system configured to receive one or moresignals indicative of a voltage associated with each energy storage unitof the plurality of energy storage units. The control system can beconfigured to send one or more command signals to selectively coupleeach energy storage unit to one of the plurality of buses based at leaston the voltage associated with the energy storage unit.

Another example aspect of the present disclosure is directed to a methodof controlling an energy storage system. The energy storage systemincludes a plurality of energy storage units and a plurality of buses.The method includes receiving, by one or more control devices, one ormore signals indicative of a voltage associated with each of theplurality of energy storage units. The method further includesdetecting, by the one or more control devices, a change in the voltageof at least one of the plurality of energy storage units. The methodincludes sending, by the one or more control devices, one or morecommand signals to selectively coupling, by the one or more controldevices, one or more of the plurality of energy storage units among theplurality of buses such that energy storage units associated withsubstantially similar voltage are coupled to the same bus.

Yet another example aspect of the present disclosure is directed to acontrol system for an energy storage system. The control system includesone or more processors and one or more memory devices. The one or morememory devices can store computer-readable instructions that whenexecuted by the one or more processors cause the one or more processorsto perform operations. The operations include receiving one or moresignals indicative of a voltage associated with each of the plurality ofenergy storage units and detecting a change in the voltage of at leastone of the plurality of energy storage units. The operations furtherinclude sending one or more command signals to selectively couple one ormore of the plurality of energy storage units among the plurality ofbuses such that energy storage units associated with substantiallysimilar voltage are coupled to the same bus.

Variations and modifications can be made to these example aspects of thepresent disclosure.

These and other features, aspects and advantages of various embodimentswill become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the present disclosure and, together with thedescription, serve to explain the related principles.

BRIEF DESCRIPTION OF THE DRAWINGS

Detailed discussion of embodiments directed to one of ordinary skill inthe art are set forth in the specification, which makes reference to theappended figures, in which:

FIG. 1 depicts an energy storage system according to example embodimentsof the present disclosure;

FIG. 2 depicts a control system according to example embodiments of thepresent disclosure;

FIG. 3 depicts a flow diagram of an example method according to exampleembodiments of the present disclosure;

FIG. 4 depicts an energy storage unit according to example embodimentsof the present disclosure;

FIG. 5 depicts an energy storage unit according to example embodimentsof the present disclosure;

FIG. 6 depicts an energy storage unit according to example embodimentsof the present disclosure;

FIG. 7 depicts an energy storage unit according to example embodimentsof the present disclosure; and

FIG. 8 depicts a flow diagram of an example method according to exampleembodiments of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the presentdisclosure, one or more examples of which are illustrated in thedrawings. Each example is provided by way of explanation of the presentdisclosure, not limitation of the present disclosure. In fact, it willbe apparent to those skilled in the art that various modifications andvariations can be made in the present disclosure without departing fromthe scope or spirit of the present disclosure. For instance, featuresillustrated or described as part of one embodiment can be used withanother embodiment to yield a still further embodiment. Thus, it isintended that the present disclosure covers such modifications andvariations as come within the scope of the appended claims and theirequivalents.

Example aspects of the present disclosure are directed to selectivelycoupling energy storage units of an energy storage system to a pluralityof buses to improve power conversion. More particularly, an energystorage system can include a plurality of energy storage units and aplurality of buses. Each energy storage unit can be associated with avoltage and each bus can be associated with a power converter. Theenergy storage system can include a master control system that can beconfigured to send one or more command signals to selectively coupleeach energy storage unit to one of the plurality of buses based at leaston the voltage associated with the energy storage unit.

More particularly, the master control system can be configured toreceive one or more signals from each energy storage unit (and/or anindividual control systems associated therewith) indicative of a voltageassociated with each of the energy storage units. Based at least on thevoltage, the master control system can be configured to send one or morecommand signal to selectively couple and/or de-couple (e.g., viaswitches, contactors, or other elements) each energy storage unit to oneor more buses. Moreover, the master control system can be configured togroup each energy storage unit such that energy storage units ofsubstantially similar voltages are included in a same group. The mastercontrol system can be configured to send one or more command signals tocouple energy storage units within the same group to the same bus tobalance the open circuit voltages among the energy storage units coupledin parallel.

The master control system can also, and/or alternatively, be configuredto detect a change in a voltage associated with an energy storage unit.The change in the voltage can be, for instance, a reduction in voltagedue to an energy storage cell failure. In response to the change in thevoltage, the master control system can be configured to send one or morecommand signals to de-couple one or more energy storage units from afirst bus and to couple the one or more energy storage units to a secondbus. The second bus can be coupled to other energy storage units ofsubstantially similar voltages.

Selectively coupling energy storage units to conversion buses accordingto example aspects of the present disclosure can improve powerconversion without incurring the significant cost of individuallyconverting power for each energy storage unit. Moreover, by selectivelycoupling energy storage units of substantially similar voltages to thesame bus, the present disclosure can help balance the open circuitvoltage among the energy storage units and reduce overvoltage.

With reference now to the Figures, example embodiments of the presentdisclosure will now be discussed in detail. FIG. 1 depicts an exampleenergy storage system 100 according to example aspects of the presentdisclosure. The energy storage system 100 can be implemented in astandalone power system or can be implemented as part of a powergeneration energy system, such as a wind power generation system, solarpower generation system, gas turbine power generation system, or othersuitable system.

The energy storage system 100 can include a plurality of energy storageunits 110, such as battery energy storage units. Each energy storageunit 110 can include one or more string 112. When an energy storage unit110 includes more than one string 112, the strings 112 can be coupled inparallel. Additionally, and/or alternatively, the plurality of energystorage units can be coupled in parallel, connecting strings ofdifferent energy storage units in parallel. Each string 112 can includea plurality of cells coupled in series. The term cell can refer to anyenergy storage device, such as, for example, a battery cell, fuel cell,electrochemical cell, rechargeable cell, ultrabattery, SMES,accumulator, capacitor, pack, etc. The energy storage unit 110 cancontain one or more sodium nickel chloride batteries, sodium sulfurbatteries, lithium ion batteries, nickel metal hydride batteries, sodiummetal halide batteries or other similar devices. Three energy storageunits, each with three strings, are illustrated in FIG. 1 for purposesof illustration and discussion. Those of ordinary skill in the art,using the disclosures provided herein, will understand that any numberof energy storage units and/or strings can be used in the energy storagesystem 100 within deviating from the scope of the present disclosure.

Each energy storage unit 110 can include a control system 120, such as abattery management system (BMS). The control systems 120 can include oneor more electronic control devices that monitor the plurality of thestring(s) 112, such as by protecting the string(s) 112 from operatingoutside a safe operating mode, monitoring a state of the cells,calculating and reporting operating data for the cells, controlling thecells environment, and/or any other suitable control actions. Forexample, in several embodiments, the control systems 120 are configuredto monitor and/or control operation of the string(s) 112, as describedin further detail herein. The control systems 120 can also be configuredto send and/or receive one or more signals. For instance, each controlsystem 120 can be configured to monitor a voltage associated with one ormore string(s) 112 and/or energy storage unit 110 and to send one ormore signals indicative of the voltage associated with the energystorage unit 110. The control systems 120 can be, for example, a logiccontroller implemented purely in hardware, a firmware-programmabledigital signal processor, or a programmable processor-basedsoftware-controlled computer.

The energy storage system 100 can include a plurality of powerconverters 130. The power converters 130 can each be configured toconvert a DC voltage associated with an energy storage unit 110 tosuitable AC power for the AC grid (e.g. 50 Hz or 60 Hz power). In someembodiments, the power converters 130 can include a combination of DC toDC converters and DC to AC converters.

The power converters 130 can include one or more electronic switchingelements, such as insulated gate bipolar transistors (IGBTs). Theelectronic switching elements can be controlled (e.g., using pulse widthmodulation) to charge or to discharge the energy storage units 110. Inaddition, the electronic switching elements can be controlled to convertthe DC power received or provided to the energy storage units 110 tosuitable AC power for application to utility grid 150 (e.g., 50 Hz or 60Hz AC power). The power converters 120 can provide AC power to the grid150 through a suitable transformer 140 and various other devices, suchas switches, relays, contactors, etc. used for protection of the energystorage system 100.

The energy storage system 100 can include a plurality of buses 160. Eachbus 160 can be associated with an individual power converter 130. Eachenergy storage unit 110 can be coupled to a bus 160. For instance, theenergy storage system 100 can include a one or more switches 170. Theone or more switches 170 can be configured to couple and/or de-coupleone or more energy storage units 110 to one or more buses 160, asfurther described herein. The number of buses, power converters, andswitches are illustrated in FIG. 1 for purposes of illustration anddiscussion. Those of ordinary skill in the art, using the disclosuresprovided herein, will understand that any number of these components canbe used in the energy storage system 100 without deviating from thescope of the present disclosure.

The energy storage system 100 can include a master control system 200that is configured to monitor and/or control various aspects of theenergy storage system 100 as shown in FIGS. 1 and 2. In accordance withvarious embodiments, the master control system 200 can include one ormore control devices or separate units or can be part of the controlsystems 120 of the energy storage units 110.

As shown, the master control system 200 can be in communication with theenergy storage units 110, control systems 120, power converters 130,buses 160, and/or switches 170. The master control system 200 can beconfigured to send and/or receive one or more signals to and/or from theenergy storage units 110, control systems 120, power converters 130,buses 160, and/or switches 170. For instance, the control systems 120and/or energy storage units 110 can be configured to send one or moresignals indicative of the voltage associated with the energy storageunit 110 to the master control system 200. The master control system 200can be configured to receive the one or more signals from the energystorage units 110 and/or the control systems 120 indicative of a voltage(e.g., an open circuit voltage) associated with each of the energystorage units 110.

The master control system 200 can be configured to send one or morecommand signals to each energy storage unit 110 and/or control system120. For instance, the master control system 200 can be configured tosend one or more command signals to each energy storage unit 110 and/orcontrol system 120 to selectively couple and/or de-couple each energystorage unit 110 to one or more of the plurality of buses 160 based atleast in part on the voltage associated with the energy storage unit110. The master control system 200 can send one or more command signalsto the energy storage 110 and/or control system 120 to couple the energystorage unit 110 to a bus 160A, 160B, 160C. The energy storage unit 110and/or control system 120 can receive the one or more command signalsand can adjust the switch 170 to couple the energy storage unit 110 to abus 160A, 160B, 160C. For instance, the control system 120 can beconfigured to adjust the switch 170 to an open position (e.g., that doesnot allow current to flow from the energy storage unit 110 through thebus 160) and/or a closed position (e.g., that allows current to flowfrom the energy storage unit 110 through the bus 160) with respect toeach of bus 160A, 160B, 160C. By way of example, to de-couple the energystorage unit 110 from the bus 160A, the control system 120 can adjustthe switch 170 to be in an open position with respect to bus 160A. Tocouple the energy storage unit 110 to bus 160B, the control system 120can adjust the switch 170 to be in a closed position with respect to bus160B.

Additionally and/or alternatively, the master control system 200 can beconfigured to group each energy storage unit 110 based at least on thevoltage associated with each energy storage unit 110. For instance, themaster control system 200 can be configured to group each energy storageunit 110 such that energy storage units associated with substantiallysimilar voltages are included in a same group (e.g., similar opencircuit voltage groups). In some embodiments, the number of groups canbe equal to the number of power converters. The master control system200 can be configured to send one or more command signals to the energystorage units 110 to couple the energy storage units within the samegroup to the same bus 160. The control system 120 may adjust the switch170, according to the one or more command signals, such that an energystorage unit 110 is coupled to the same bus as other energy storageunits in the group. The energy storage units 110 may be assigned todifferent groups over time as the energy storage units 110 degrade atdifferent rates or if one or more energy storage units 110 are added toand/or replaced in the energy storage system 100.

The master control system 200 can be configured to detect a change in avoltage of the energy storage unit 110. For instance, the master controlsystem 200 can be configured to detect a change in the voltage based onone or more signals received from the energy storage units 110 and/orthe control systems 120. In response to the change in voltage, themaster control system 200 can be configured to send one or more commandsignal to de-couple one or more energy storage unit 110 from a first bus160A (e.g., by adjusting the switch 170 from a closed position to anopen position with respect to bus 160A) and to couple the one or moreenergy storage units 110 to a second bus 160B (e.g., by adjusting theswitch 170 from an open position to a closed position with respect tobus 160B). The second bus 160B can be coupled to other energy storageunits associated with substantially similar voltages. In this way, themaster control system 200 can help prevent overvoltage conditions.

Referring particularly to FIG. 2, the master control system 200 can haveany number of suitable control devices. The master control system 200can include a system level controller for the energy storage system 100and/or a controller of one or more individual energy storage unit 110 orcontrol system 120. As shown, for example, the master control system 200(and/or control system 120) can include one or more processor(s) 212 andone or more memory device(s) 214 configured to perform a variety ofcomputer-implemented functions and/or instructions (e.g., performing themethods, steps, calculations and the like and storing relevant data asdisclosed herein). The instructions when executed by the processor(s)212 can cause the processor(s) 212 to perform operations according toexample aspects of the present disclosure. For instance, theinstructions when executed by the processor(s) 212 can cause theprocessor(s) 212 to implement one or more control interfaces.

Additionally, the master control system 200 can include a communicationsinterface 216 to facilitate communications between the master controlsystem 200 and the various components of the energy storage system 100.For example, the communications interface can permit the transmission ofsignals to and/or from energy storage units 110, control systems 120,power converters 130, buses 160, and/or switches 170. The signals can becommunicated using any suitable communications protocol. As such, theprocessor(s) 212 can be configured to receive and/or send one or moresignals from the energy storage units 110, control systems 120, powerconverters 130, buses 160, and/or switches 170.

As used herein, the term “processor” refers not only to integratedcircuits referred to in the art as being included in a computer, butalso refers to a controller, a microcontroller, a microcomputer, aprogrammable logic controller (PLC), an application specific integratedcircuit, and other programmable circuits. Additionally, and/oralternatively, the memory device(s) 214 can generally include memoryelement(s) including, but not limited to, computer readable medium(e.g., random access memory (RAM)), computer readable non-volatilemedium (e.g., a flash memory), a compact disc-read only memory (CD-ROM),a magneto-optical disk (MOD), a digital versatile disc (DVD) and/orother suitable memory elements. Such memory device(s) 214 can generallybe configured to store suitable computer-readable instructions that,when implemented by the processor(s) 212, configure the master controlsystem 200 to perform the various functions as described herein.

FIG. 3 depicts a flow diagram of an example method 300 for controllingan energy storage system according to example embodiments of the presentdisclosure. The method can be implemented in any suitable energy storagesystem, such as the energy storage system 100 of FIG. 1. In addition,FIG. 3 depicts steps performed in a particular order for purposes ofillustration and discussion. Those of ordinary skill in the art, usingthe disclosures provided herein, will understand that various steps ofany of the methods disclosed herein can be omitted, rearranged,modified, expanded, or adapted in various ways without deviating fromthe scope of the present disclosure.

At (302), the method includes receiving one or more signals indicativeof a voltage associated with each of the plurality of energy storageunits 110. For instance, the control systems 120 can monitor a voltageassociated with the energy storage units 110 and/or string(s) 112. Thecontrol systems 120 and/or energy storage units 110 can send one or moresignals indicative of the voltage associated with an energy storage unit110 to the master control system 200. The master control system 200 canreceive one or more signals, for instance, from the each energy storageunit 110 and/or control system 120, indicative of a voltage (e.g., opencircuit voltage) associated with each of the energy storage units 110.

At (304), the method includes detecting a change in the voltage of atleast one of the plurality of energy storage units 110. For instance,the master control system 200 can detect a change in the voltage. Thechange in the voltage can be a reduction in voltage (e.g., open circuitvoltage) due to a cell failure. In example embodiments, the mastercontrol system 200 can detect the change in the voltage based on the oneor more signals received by the master control system 200. In addition,and/or in the alternative, the master control system 200 can monitor avoltage associated with each energy storage unit 110 and detect a changein voltage based on such monitoring.

At (306), the method includes sending one or more command signal toselectively couple one or more of the plurality of energy storage units110 among the plurality of buses 160 such that energy storage units 110associated with substantially similar voltage are coupled to the samebus 160. The master control system 200 can send one or more commandsignal to the energy storage units 110 and/or control systems 120 toselectively couple each energy storage unit 110 to a bus 160 by, forinstance, closing a switch 170. Each energy storage unit 110 can becoupled to a bus 160 such that energy storage units associated withsubstantially similar voltages are coupled to the same bus.

As one example, the method 300 can include grouping each energy storageunit 110 based at least on the voltage associated with each energystorage unit 110, such that energy storage units associated withsubstantially similar voltages are included in a same group. The method300 can include sending one or more command signal to couple the energystorage units 110 within the same group to the same bus. The mastercontrol system 200 can group each energy storage unit 110 such thatenergy storage units associated with substantially similar voltages canbe included in the same group. Moreover, the master control system 200can send one or more command signals to the energy storage units 110and/or control systems 120 to couple (e.g., via the switches,contactors, or other elements) the energy storage units 110 within thesame group to the same bus. In this way, the master control system 200can help prevent overvoltage.

As another example, the method 300 can include sending one or morecommand signals to de-couple one or more energy storage units 110 from afirst bus 160A and sending one or more command signals to couple the oneor more energy storage units 110 to a second bus 160B of the pluralityof buses in response to the change in the voltage. The master controlsystem 200 can send one or more command signals (e.g., to the energystorage units 110 and/or control systems 120) to de-couple one or moreenergy storage units 110 from a first bus 160A. For instance, the energystorage units 110 and/or control systems 120 can de-couple the energystorage units 110 from a first bus 160A by adjusting the switch 170 froma closed position to an open position with respect to the first bus160A.

The master control system 200 can send one or more command signals(e.g., to the energy storage units 110 and/or control systems 120) tocouple the energy storage unit 110 to a second bus 160B in response tothe change in the voltage. For instance, based on the change in voltage(e.g., a reduction in voltage) the master control system 200 can selecta second bus 160B that can be coupled to one or more energy storageunits associated with substantially similar voltages as the energystorage unit 110 associated with the change in voltage. The energystorage unit 110 and/or control system 120 can couple the energy storageunit 110 to the second bus 160B by adjusting the switch 170 from an openposition to a closed position with respect to second bus 160B. In thisway, the master control system 200 can help prevent overvoltage of anenergy storage unit 110 that experiences a change in voltage (e.g.,reduction in voltage).

FIGS. 4-7 depict an example energy storage unit 110 according to exampleaspects of the present disclosure. The energy storage unit 110 caninclude one or more strings 112A, 112B and a control system 120 (e.g., abattery management system). In the event that the energy storage unithas more than one string, the strings 112A, 112B can be coupled inparallel. Each string 112A, 112B can include a plurality of cells 113,114 coupled in series. In FIGS. 4-7 and/or the embodiments describedherein, the strings 112A and 112B can be associated with the same energystorage unit 110 and/or difference energy storage units 110.Additionally, and/or alternatively, as shown in FIGS. 4-7 and describedherein, the control system 120 can include one or more control devicesof an energy storage unit 110 and/or one or more control devices ofdifferent energy storage units 110.

Each string 112A, 112B can be associated with a selectively adjustabletap location to control the number of cells 113, 114 in the string thatprovide power to a power system. While each cell 113, 114 can beconfigured to provide power to a power system, the control system 120can control which of the cells 113, 114 do, in fact, provide power tothe power system by adjusting the tap location. For instance, each cell113, 114 can be associated with a tap 115, 116 (e.g., switch,transistor, contactor, etc.) configured to prevent and/or allow thecells 113, 114 (and all cells previously in series) to provide power toa power system. The tap location can be a location at which a tap isclosed, thereby allowing cells to provide power through a tap.

By way of example, as shown in FIG. 4, tap 115B is closed and can allowcells 113A and 113B (and any cells coupled in series below 113A) toprovide power to a power system, through tap 115B. Tap 115C is open andcan prevent cell 113C from providing power to a power system. The taplocation can be associated with the location of tap 115B through whichthe cells 113A, 113B (and any cells coupled in series below 113A) canprovide power to a power system. In this way, the cells 113A, 113B canbe included in the number of cells that provide power to a power system,while cell 113C can be excluded from the number of cells that providepower to a power system.

The control system 120 can be configured to be in communication witheach of the string(s) 112 and the taps 115, 116. The control system 120can be configured to monitor a voltage associated with each of thestring(s) 112A, 112B and to detect a change in a voltage associated withone or more of the string(s) 112A, 112B. The change in the voltage canbe a reduction in voltage associated with a cell failure. The controlsystem 120 can be configured to adjust the tap location for at least oneof the string(s) 112A, 112B in response to the change in the voltage.

In one example, one or more energy storage units 110 can include a firststring 112A comprising a first plurality of cells 113A, 113B, 113Ccoupled in series and a second string 112B comprising a second pluralityof cells 114A, 114B, 114C coupled in series. The first string 112A andthe second string 112B can be coupled in parallel. If a first cell 113Bof the first string 112A fails (e.g., fails short) there can be a changein the voltage (e.g., a reduction in the voltage) associated with thefirst string 112A. The control system 120 can detect the change in thevoltage and can be configured to adjust the tap location for at leastone of the string(s) 112A, 112B to balance the open circuit voltage.

For instance, when the change in the voltage is a voltage reductionassociated with the first string 112A, the control system 120 can beconfigured to adjust the tap location associated with the first string112A to increase the number of cells 113 of the first string 112A thatprovide power through the tap location. The control system 120 canadjust the tap location associated with the first string 112A byadjusting a first tap 115B from a closed position (e.g., FIG. 4) to anopen position (e.g., FIG. 5) and adjusting a second tap 115C from anopen position (e.g., FIG. 4) and to a closed position (e.g., FIG. 5).Such adjustment can allow cell 113C to provide power through the taplocation (e.g., at the closed second tap 115C of FIG. 5). In this way,the voltage associated with the first string 112A can be increased suchthat it can be substantially similar to the voltage associated with thefirst string 112A prior to the cell failure. Moreover, by adjusting thetap location associated with the first string 112A, the control system120 can balance the open circuit voltage among the plurality of stringssuch that the open circuit voltages among the plurality of strings aresubstantially similar (e.g., within 20% of each other). For instance,the voltage of the first string 112A can be substantially similar to thevoltage of the second string 112B. Such balancing can help avoidovervoltage of the first string 112A.

Additionally and/or alternatively, when the first string 112Aexperiences a change in voltage (e.g., reduction in voltage), thecontrol system 120 can be configured to reduce the voltage associatedwith the second string 112B. For instance, the control system 120 canadjust the tap location associated with the second string 112B todecrease the number of cells 114 of the second string 112B that providepower through the tap location. The control system 120 can adjust thetap location associated with the second string 112B by adjusting a firsttap 116B from a closed position (e.g., FIG. 6) to an open position(e.g., FIG. 7) and adjusting a second tap 116A from an open position(e.g., FIG. 6) to a closed position (e.g., FIG. 7). Such adjustment canprevent the cell 114B from providing power through the tap location(e.g., at the closed second tap 116A) and can reduce the voltageassociated with the second string 112B. The voltage associated with thesecond string 112B can be reduced such that it is substantially similarto the voltage associated with the first string 112A after the cellfailure. Additionally, and/or alternatively, the control system 120 canadjust a tap location associated with each string (other than the firststring 112A) of the plurality of strings in a similar manner to reducethe voltage associated with each string. In this way, the control system120 can balance the open circuit voltages among the plurality of stringssuch that the open circuit voltages among the plurality of strings aresubstantially similar.

FIG. 8 depicts a flow diagram of an example method 800 for controlling atap location associated with an energy storage unit according to exampleembodiments of the present disclosure. The method 800 can be implementedin any suitable energy storage unit, such as the energy storage unit 110of FIGS. 4-7. In addition, FIG. 8 depicts steps performed in aparticular order for purposes of illustration and discussion. Those ofordinary skill in the art, using the disclosures provided herein, willunderstand that various steps of any of the methods disclosed herein canbe omitted, rearranged, modified, expanded, or adapted in various wayswithout deviating from the scope of the present disclosure.

At (802), the method 800 includes monitoring a voltage associated with afirst string 112A comprising a first plurality of cells 113 coupled inseries. At (804), the method 800 includes monitoring a voltageassociated with a second string 112B comprising a second plurality ofcells 114 coupled in series. The first string 112A and the second string112B can be coupled in parallel. For instance, a control system 120 canmonitor the voltage associated with the first string 112A and/or thevoltage associated with the second string 112B. The voltage can be anopen circuit voltage. In addition, and/or in the alternative, thecontrol system 120 can monitor a voltage associated with one or morecells of the first and/or second plurality of cells 113, 114.

At (806), the method 800 includes detecting a change in a voltageassociated with the first string 112A. For instance, the control system120 can detect a change in the voltage associated with the first string112A. The change in the voltage can be a voltage reduction associatedwith the first string 112A that can occur when a cell 113 fails (e.g.,fails short).

At (808), the method 800 includes adjusting a tap location for the firststring 112A or second string 112B in response to the change in thevoltage. For instance, the control system 120 can adjust a tap locationfor the first string 112A and/or second string 112B. In one example, themethod 800 can include adjusting the tap location associated with thefirst string 112A to increase the number of cells that provide powerthrough the tap location associated with the first string 112A. Prior tothe change in the voltage of the first string 112A, the first string112A can be associated with a tap location at a first tap 115B that isclosed, as shown in FIG. 4. When the voltage associated with the firststring 112A changes (e.g., reduces), the control system 120 can adjustthe tap location associated with the first string 112A by adjusting thefirst tap 115B from a closed position to an open position and adjustinga second tap 115C from an open position to a closed position, as shownin FIGS. 4 and 5. By adjusting the tap location to the second tap 115C,the control system 120 can allow an additional cell 113C (that was notproviding power through the tap location prior to the change in voltage)to provide power through the tap location (e.g., at the closed secondtap 115C). In this way, the control system 120 can increase the voltageassociated with the first string 112A and balance the open circuitvoltage among the plurality of strings.

In addition, and/or in the alternative, the method 800 can includeadjusting the tap location for the second string 112B to decrease thenumber of cells 114 that provide power through the tap location for thesecond string 112B. For instance, prior to the change in the voltageassociated with the first string 112A, the second string 112B can have atap location at a first tap 116B, as shown in FIG. 6. When the voltageassociated with the first string 112A changes (e.g., reduces), thecontrol system 120 can adjust the tap location associated with thesecond string 112B by adjusting the first tap 116B from a closedposition to an open position and adjusting a second tap 116A from anopen position to a closed position, as shown in FIGS. 6 and 7. The taplocation can now be associated with the closed second tap 116A and canprevent cell 114B (that was previously providing power prior to thechange in voltage of first string 112A) from providing power through thetap location (e.g., at second tap 116A). In this way, the control system120 can decrease the voltage associated with the second string 112B andbalance the open circuit voltages of the first and second string(s)112A, 112B.

Although specific features of various embodiments can be shown in somedrawings and not in others, this is for convenience only. In accordancewith the principles of the present disclosure, any feature of a drawingcan be referenced and/or claimed in combination with any feature of anyother drawing.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and can include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. An energy storage system, comprising: a pluralityof energy storage units; a plurality of buses; and a control systemconfigured to receive one or more signals indicative of a voltageassociated with each energy storage unit of the plurality of energystorage units, wherein the control system is configured to send one ormore command signals to selectively couple each energy storage unit toone bus of the plurality of buses based at least on the voltageassociated with each energy storage unit of the plurality of energystorage units.
 2. The energy storage system of claim 1, wherein thecontrol system is configured to send one or more command signals toselectively couple each energy storage unit to one bus of the pluralityof buses such that energy storage units of the plurality of energystorage units with substantially similar voltages are coupled to a samebus.
 3. The energy storage system of claim 1, wherein the voltage is anopen circuit voltage (OCV).
 4. The energy storage system of claim 1,wherein each bus of the plurality of buses is associated with a powerconverter.
 5. The energy storage system of claim 1, wherein theplurality of buses comprises a first bus and a second bus.
 6. The energystorage system of claim 5, wherein the control system is configured tosend one or more command signals to decouple a first energy storage unitof the plurality of energy storage units from the first bus and to sendone or more command signals to couple the first energy storage unit tothe second bus in response to a change in the voltage associated withthe first energy storage unit.
 7. The energy storage system of claim 6,wherein the change in the voltage is a reduction in the voltage.
 8. Amethod of controlling an energy storage system, the energy storagesystem comprising a plurality of energy storage units and a plurality ofbuses, the method comprising: receiving, by one or more control devices,one or more signals indicative of a voltage associated with each energystorage unit of the plurality of energy storage units; detecting, by theone or more control devices, a change in the voltage of at least oneenergy storage unit of the plurality of energy storage units; andsending, by the one or more control devices, one or more command signalsto selectively couple one or more energy storage units of the pluralityof energy storage units among the plurality of buses such that energystorage units of the plurality of energy storage units withsubstantially similar voltages are coupled to a same bus.
 9. The methodof claim 8, wherein the sending comprises: sending one or more commandsignals to decouple the one or more energy storage units from a firstbus of the plurality of buses, and sending one or more command signalsto couple the one or more energy storage units to a second bus of theplurality of buses in response to the change in the voltage.
 10. Themethod of claim 8, wherein the sending comprises: grouping each energystorage unit of the plurality of energy storage units based at least onthe voltage associated with each energy storage unit such that energystorage units of the plurality of energy storage units withsubstantially similar voltages are included in a same group, and sendingone or more command signals to couple the energy storage units withinthe same group to a same bus.
 11. The method of claim 8, wherein thevoltage is an open circuit voltage (OCV).
 12. The method of claim 8,wherein the change in the voltage is a reduction in the voltage.
 13. Themethod of claim 8, wherein the change in the voltage is associated witha cell failure.
 14. The method of claim 8, wherein each bus of theplurality of buses is associated with a power converter of a pluralityof power converters.
 15. A control system for an energy storage system,the control system comprising one or more processors and one or morememory devices, the one or more memory devices storing computer-readableinstructions that, when executed by the one or more processors, causethe one or more processors to perform operations, the operationscomprising: receiving one or more signals indicative of a voltageassociated with each energy storage unit of a plurality of energystorage units; detecting a change in the voltage of at least one energystorage unit of the plurality of energy storage units; and sending oneor more command signals to selectively couple one or more energy storageunits of the plurality of energy storage units among the plurality ofbuses such that energy storage units of the plurality of energy storageunits with substantially similar voltages are coupled to a same bus. 16.The control system of claim 15, wherein the operation of sendingcomprises: sending one or more command signals to decouple the one ormore energy storage units from a first bus of the plurality of buses,and sending one or more command signals to couple the one or more energystorage units to a second bus of the plurality of buses in response tothe change in the voltage associated with the one or more energy storageunits.
 17. The control system of claim 15, wherein the operation ofsending comprises: grouping each energy storage unit of the plurality ofenergy storage units based at least on the voltage associated with eachenergy storage unit, such that energy storage units associated withsubstantially similar voltages are included in a same group, and sendingone or more command signals to couple the energy storage units withinthe same group to a same bus.
 18. The control system of claim 15,wherein the voltage is an open circuit voltage (OCV).
 19. The controlsystem of claim 15, wherein the change in the voltage is a reduction inthe voltage.
 20. The control system of claim 15, wherein each bus of theplurality of buses is associated with a power converter of a pluralityof power converters.